Add the numbers together.
For example, if you need to find the average of -2, -3, -4 and -1, adding these numbers will give you -10. Remember that the sum of a series of negative numbers is always negative.
Count the number of terms (numbers) that you added. In the example, there were four numbers. Counted numbers are always positive, so the answer to this step is positive 4.
Divide the sum by the number of terms. The answer is called the arithmetic mean, or average, of these numbers.
In the example problem, -10 / 4 = -2.5.